Watch this video of current big city mayors talking about why no one has ever moved from sitting mayor to American President. The most common reason given: mayors have to make decisions, big and small and often pragmatic, all the time and this doesn’t line up with the gotcha politics of today and keeping all the constituents happy. It may be just me reading into the video but it seems like these mayors give this reason with both a sense of pride and regret: “Hey, we make tough decisions all the time and this can make people mad. Unfortunately, we don’t get rewarded at the highest level for such choices.”
I suspect there is more to this story, particularly if we asked the mayors of the biggest cities, and it would be worth hearing more.